More modbus extensions



  • Hi do you have some manual how I can connect more Modbus extensions? I have xS40 and it works fine with my M303. But when I connect another xS40 I cannot connect it via Modbus. There is no connection. I try sett up addresses on pins, setup Mervis, but LED diodes for connection are off.


  • administrators

    @SorakCz Baudrate and parity have to be same for the whole bus but addresses have to be different.

    If you have address 0 configured via DIP switches, then the Extensions are using SW address (which can be changed via modbus registers). If you use any other addres via DIP switches, then the DIP switch configuration is also used for baudrate and parity.

    So: Decide which baudrate and parity you want to use (eg, start with 9600, N), configure it in Mervis and on both extensions, and select different addresses. Also do not forget to set address of extensions in Mervis.



  • i think I have all setted. I changed address on the extensions, restart extension, upload program and it dont work.
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  • administrators

    @SorakCz The extensions are configured to use Even parity but in the IDE, the parity is None. Those have to be the same too. Also, make sure to power cycle the extensions after you make a change in the DIP switch configuration.



  • Parity is pin 8? I will try it. What is better? Parity no or yes?

    Thank You


  • administrators

    @SorakCz Yes, its pin 8. It depends on the application. Parity helps to detect an error in a word on the line. Its either None(disabled) or Even in this case...



  • Thank you Tomas, it was very helpful. Now it working. I only switch off parity on external modules and communication started :-)